1. Field of the Invention
The present invention relates to a magazine for storing mini chips that are to be fitted to distal ends of chip bases of a spot welder.
2. Description of Related Art
Conventionally, spot welding has been widely used as one means for welding metal workpieces, wherein, with the metal workpieces being pressed together, electric current is applied, so as to melt and fuse the metal with the resistance heat. An automated welding line for spot welding body parts of cars is made up of a robot equipped with a welding gun, and a jig for securing and moving a workpiece to be welded. Alternatively, an automated welding line is made up of a stationary welding gun, and a robot that holds a workpiece to be welded and moves this workpiece to be welded toward the stationary welding gun.
The welding gun, as shown in FIG. 15, has opposing arms 190 and 191, with cap chips 195 fitted to the mounting portions 190a and 191a formed at the distal ends of the arms. In a process in which welding is performed using a welding gun mounted on a robot, the robot is operated to move the opposing arms 190 and 191 to a weld spot 252 of workpieces to be welded 250 and 251, and while the cap chips 195 are pressed against the workpieces to be welded 250 and 251, electric current is applied so as to weld the workpieces 250 and 251 together. Alternatively, in a process in which welding is performed using a stationary welding gun, the workpieces to be welded 250 and 251 are moved by the robot to the position between the opposing arms 190 and 191, and while the cap chips 195 are pressed against the weld spot 252 of the workpieces to be welded 250 and 251, electric current is applied so as to weld the workpieces 250 and 251 together.
In a welding gun such as the one shown in FIG. 15, when there is present a member 255 near the workpiece to be welded 250, the arm 190 and cap chip 195 cannot fit in between the workpiece to be welded 250 and the member 255 due to the large dimension α from the base of the mounting portion 190a to the distal end of the cap chip 195, so the workpieces 250 and 251 cannot be welded together. Therefore, for such welding spots, a chip base 301 such as the one shown in FIG. 16 is commonly used instead of the arm 190.
A mini chip 302 is mounted to the distal end of the chip base 301. FIG. 17 shows a detailed view of the chip base 301, and FIG. 18 shows a detailed view of the mini chip. As shown in FIG. 17, the chip base 301 has a plate-like shape, and the mini chip 302 is mounted in a mounting hole 301a formed at the distal end of the chip base 301 such as to extend therethrough. Therefore the thickness dimension β from the distal end of the chip base 301 to an abutment portion 302a of the mini chip 302 is small, so that even in a narrow space where there is present a member 255 close to the workpiece to be welded 250, the mini chip 302 can be moved to the weld spot 252 and the workpieces 250 and 251 can be welded together.
Performing the spot welding more than a predetermined number of times causes the distal end shape of the abutment portion 302a of the mini chip 302 or the cap chip 195 to suffer deformation and wear, making it harder to secure required welding quality. Therefore, when a certain period of processing time or a certain number of welding points is exceeded, the mini chip 302 or cap chip 195 need to be removed and replaced with new ones or those that have undergone a grinding treatment.
Conventionally, an operator would go inside the automated welding line that had been paused, and remove the cap chip 195 by inserting a tool for removing electrode chips such as the one shown in Patent Document 1 to the distal end of the arm 191, or remove the mini chip 302 by hitting its mounting portion 302b through the mounting hole 301a of the chip base 301. However, it was very dangerous for the operator to go inside the automated welding line, as it meant going inside a movable range of the robot arm. Also, for the operator to go inside the automated welding line, it was necessary to stop the automated welding line, which led to the problem that production efficiency was deteriorated. Further, in recent years, many of the materials to be welded are provided with rust proof treatment or the like using chemicals, because of which mini chips 302 and cap chips 195 tend to wear more quickly and need to be replaced more frequently. However, stopping the automated welding line each time to replace the mini chip 302 or cap chip 195 would lead to the problem of production efficiency being largely deteriorated.
Accordingly, a welder cap chip removing apparatus has been proposed as shown in Patent Document 2. This welder cap chip removing apparatus is made up of a fixed claw to be inserted into the distal end of the arm 191, a movable claw rotatably attached to a base end of this fixed claw such as to contact and separate from the fixed claw, and a rotating Mechanism that applies a rotating force to the movable claw. To remove the cap chip 195, the robot arm is moved to insert the distal end of the arm 191 in between the fixed claw and movable claw, and when the movable claw is separated from the fixed claw, the cap chip 195 is removed from the arm 191.
When using this welder cap chip removing apparatus shown in Patent Document 2, a magazine rack for a chip changer such as the one shown in Patent Document 3 is used for storing replacement cap chips. This magazine rack for a chip changer shown in Patent Document 3 is formed such that a plurality of cap chips 195 are stored inside a long columnar rack body and fed one by one to a supply port. With this magazine rack for a chip changer installed near the robot arm, a cap chip 195 can be automatically mounted to the arm 191 by moving the welding gun using the robot arm to insert the mounting portion 191a of the arm 191, from which the cap chip 195 has been removed, into the supply port of the magazine rack for a chip changer. By thus using the welder cap chip removing apparatus shown in Patent Document 2 and the magazine rack for a chip changer shown in Patent Document 3, automatic mounting and dismounting of cap chips 195 to and from the arm 191 of the welding gun in an automated welding line would be possible.
However, while the welder cap chip removing apparatus shown in Patent Document 2 can remove cap chips 195, it cannot remove mini chips 302, and therefore if there is even one process step in which mini chips 302 are used in the automated welding line, the automated welding line would still be stopped, as had been conventionally done, for the operator to go inside the automated welding line to remove the mini chip 302 from the chip base 301 and mount a new mini chip 302 to the chip base 301. Accordingly, the problem of the operator being exposed to danger, or the problem that the production efficiency of the automated welding line was largely deteriorated, would remain unsolved. Therefore, development of a magazine for spot welding chip for storing mini chips as well as a mini chip removing apparatus has been desired.
Patent Document 1: Japanese Published Unexamined Patent Application No. H11-123565
Patent Document 2: PCT/JP2004/011688
Patent Document 3: Japanese Published Unexamined Patent Application No. 2006-68787